Qualitative observations are reported of macroscopic changes in polyvinyl acetate gels that occur upon removal from swelling equilibrium with isopropyl alcohol by lowering the temperature below the (upper) Θ point (54.7°C). In addition to syneresis, all systems exhibit turbidity, the extent of which depends on the degree of supercooling, the "curing," i.e., aging time (being different from the crosslinking time), and the network density. The development of turbidity is thought to be due either to microsyneresis, i.e., polymer-diluent incompatibility on microscale or local deformation of the network resulting in structural inhomogeneity. This is in most cases so pronounced that separation of a turbid "core" and a more transparent "crust" takes place. On the basis of phase diagrams constructed from cloud point data the network density was found to be of no detectable influence upon phase behavior being at variance with existing theory. Finally, phase diagrams of polystyrene gels swollen in methyl acetate were determined in the vicinity of both the upper and lower Θ temperatures (43 and 114°C, resp.). The shape of those phase diagram sections which are experimentally available for polyvinyl acetate and polystyrene gels was found to be similar to that of the solutions of these polymers in the same solvent.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films
- Colloid and Surface Chemistry